The present invention relates to a control method for adjusting the hydrocarbon concentration in an active carbon filter of a tank ventilation device of a motor vehicle, including the detection of an operational parameter of the internal combustion engine of the motor vehicle.
Such a control method is known, for instance, from DE 101 31 798 A1, in which is described a regeneration device for regenerating an active carbon filter. The regeneration device is activated when the internal combustion engine is in an overrun mode that is detected by the control method. The so-called loading status of the active carbon filter is determined by way of measured values that are detected on a lambda probe arranged downstream of the internal combustion engine. The loading state of the active carbon filter may thus only be determined using a gas mixture that is flowing downstream of the combustion engine and that is supplied to the exhaust treatment system.
The object of the invention is to provide a control method that permits more precise determination of the loading of the active carbon filter and offers additional options for regenerating the active carbon filter.
For attaining this object, a control method is provided that includes the following acts:
a) determining a hydrocarbon content of a tank gas mixture in the tank ventilation device; and
b) opening a tank ventilation valve of the tank ventilation device for a defined length of time as a function of the determined hydrocarbon content, when the operational parameter of the internal combustion engine indicates an overrun mode or a standstill caused by a start-stop system of the internal combustion engine.
The determination of the hydrocarbon content in the tank ventilation device, which is arranged upstream of the internal combustion engine in terms of flow, permits improved and more precise determination of how strongly the active carbon filter is loaded with hydrocarbons. From this it is also possible to determine more precisely the need for regenerating the active carbon filter. Since the hydrocarbon content in the tank ventilation device is known, the active carbon filter may be regenerated not only during overrun operation of the internal combustion engine, but also during a temporary standstill thereof that is caused by a start-stop system.
In one refinement, the method detects the temperature of an exhaust treatment system of the motor vehicle, wherein the defined length of time the tank ventilation valve is opened is a function of the detected temperature of the exhaust treatment system.
This is intended to include, in particular, the temperature of a catalytic converter arranged downstream of the internal combustion engine. The normal operational temperature of a catalytic converter is about 300° C. to 800° C. The temperature of the catalytic converter is thus a function of the speed and load of the internal combustion engine. At appropriate temperatures in the catalytic converter, the supply to the catalytic converter of hydrocarbons that have not been combusted (or only some of which have been combusted) in the internal combustion engine in overrun mode leads to a subsequent reduction thereof in the exhaust gas flow due to oxidation or reduction.
It is preferred that the hydrocarbon content be determined by use of an HC sensor attached in the area of the tank ventilation device. The HC sensor should be arranged as best as possible such that it may determine a representative hydrocarbon content for the active carbon filter. The HC sensor is preferably disposed in a limited area between active carbon filter and tank ventilation lines that lead to and away therefrom. It is also possible for such an HC sensor to be built into an active carbon filter.
Alternatively, the hydrocarbon content may be determined by at least one characteristic value of a model for the hydrocarbon content in tank gases. Such a model may be embodied, for instance, such that it takes into account different parameters, especially determinant parameters, which affect the outgassing of the liquid fuel. With such a model, it is possible to model the hydrocarbon content of the part of a tank that is not filled with liquid fuel and the ventilation lines connected thereto. From the model, taking into account variables that may be provided by a control unit of the motor vehicle, such as for instance ambient temperature, cooling water temperature, ambient air pressure, downtimes of the combustion engine, values of acceleration sensors in the longitudinal and transverse directions, and fuel temperature, it is possible to estimate or derive values for a hydrocarbon content that is present in the tank ventilation device. It is also possible to take into account in such a model the geometry of the fuel container which, in conjunction with a fill level with liquid fuel, also has an effect on outgassing.
With the method it is further provided that the higher the temperature of the exhaust treatment system, the shorter the defined length of time for opening the tank ventilation valve. Such a control or regulation makes it possible, first of all, for the temperature of the exhaust treatment system to not be substantially changed, in particular to rise only slightly, due to introduced and chemically reacting hydrocarbons. By limiting the time the tank ventilation valve is open, it is possible for the operational temperature of the exhaust treatment system to remain in an optimal range and not rise above a maximum allowed operational temperature or drop below a minimum allowed operational temperature.
Furthermore, with the method, the length of time the tank ventilation valve is open may become shorter the higher is the hydrocarbon content. Because of this, it is possible to prevent too much hydrocarbon, especially non-combusted or only partially combusted hydrocarbon, from traveling into the exhaust system and thereby causing the temperature of the exhaust treatment system to rise too rapidly due to corresponding chemical (catalytic) reactions.
It is furthermore provided that the length of time that the tank ventilation valve is open be between 0.5 and 10 seconds, and that the temperature of the exhaust treatment system during the defined length of time the tank ventilation valve is open be between 300° C. and 800° C. The ranges disclosed here for the length of time the tank ventilation valve is open and for the temperature of the exhaust gas system may also be selected to be different as a function of the specifications and design of a control system for the internal combustion engine and the exhaust treatment system.
With the inventive control method, when the internal combustion engine of the motor vehicle is in overrun mode, when the tank ventilation valve is opened, the gas containing the hydrocarbon is preferably caused to be drawn from the tank ventilation device by a negative pressure that exists relative to the internal combustion engine. This negative pressure is affected by the opening of a throttle valve and the valves on the internal combustion engine. In this context, it is also possible for variably adjustable valves to be provided for the internal combustion engine so that enhanced control of the negative pressure in the intake area of the internal combustion engine may be attained. Using a negative pressure sensor arranged in an intake pipe, it is possible to adjust a more precise negative pressure of, for instance, approximately 100 mbar, in the intake pipe between the throttle valve and the valves during an overrun operation of the internal combustion engine. The tank ventilation valve is then only opened or closed and no additional regulation is required for how much the tank ventilation valve is opened.
Alternatively, if it is determined that the internal combustion engine is in a standstill, a tank gas pump provided in the area of the tank ventilation device may conduct the gas containing hydrocarbon to the internal combustion engine if the tank ventilation valve is opened. Instead of a tank gas pump, it is also possible to provide a compressed air reservoir that stores, for instance, negative or positive pressure from the engine operation and can provide the stored pressure in order to conduct the gas containing hydrocarbon to the internal combustion engine.
For instance, if regeneration of the active carbon filter begins immediately before a start-stop system brings the internal combustion engine to a standstill, then while the engine is at a standstill the negative pressure required for drawing the tank gases out of the tank ventilation device is lacking. However, in order to still make it possible to regenerate, even if the engine is at a standstill, during a certain length of time ventilation gases may be conducted by means of the pump or the compressed air reservoir out of the tank ventilation device into the intake manifold of the internal combustion engine or via the intake manifold through the combustion chamber into the exhaust system for a follow-on reaction. At least some of the tank ventilation gases that were introduced that remain in the intake pipe are then combusted during further operation of the internal combustion engine, in addition to an amount of fuel added (injected) into the cylinder.
For attaining the object cited in the foregoing, further provided is a motor vehicle comprising:
an internal combustion engine having at least one combustion chamber, an intake area supplying combustion air to at least one combustion chamber, and an exhaust area that draws off exhaust gasses from at least one combustion chamber;
an exhaust treatment system connected to the exhaust area of the internal combustion engine;
a tank ventilation device that opens into the intake area of the internal combustion engine and that is closed to the intake area using a tank ventilation valve; and
a control unit for controlling the combustion engine and the exhaust treatment system, wherein the control unit is embodied to control the opening of the tank ventilation valve for a defined length of time in accordance with the described control method.
In one refinement, the motor vehicle may include a sensor, especially an HC sensor, arranged in the area of the tank ventilation device and/or the control unit which may be embodied to store characteristic values of a model of the hydrocarbon content and to control the length of time the tank ventilation valve is open, taking these characteristic values into consideration.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.